R.P. George

Antibacterial copper―nickel bilayers and multilayer coatings by pulsed laser deposition on titanium

Biofouling, especially microfouling, is a major concern with the use of titanium (Ti) in the marine environment as a condenser material in cooling water systems. Earlier, copper–nickel (Cu/Ni) alloys were extensively used in marine environments due to their high corrosion and biofouling resistance. However, the choice of condenser material for the new fast breeder reactor in Kalpakkam is Ti to avoid steam side corrosion problems, which may pose a threat to steam generator parts having sodium as the secondary coolant. This study evaluates the surface modification of Ti using nano films of copper (Cu) and nickel (Ni) to utilize the antibacterial property of copper ions in reducing microfouling. The surface modification of Ti was carried out by the deposition of a Cu/Ni bilayer and (Cu/Ni)10 multilayer films using a pulsed laser deposition technique. Various surface characterization studies revealed that the deposited Cu/Ni films were thin and nanocrystalline in nature. The antibacterial properties were evaluated using total viable count and epifluorescence microscopic techniques. The results showed an apparent decrease in bacterial attachment on multilayered and bilayered Cu/Ni thin films on Ti surfaces. Comparative studies between the two types of films showed a bigger reduction in numbers of microorganisms on the multilayers.

Surface modification of type 304 stainless steel with duplex coatings for corrosion resistance in sea water environments

Abstract An attempt was made to improve the localised corrosion resistance of AISI type 304 stainless steel by modifying the surface with duplex coating (titania over ceria). Simple chemical immersion method was adopted for ceria coating, whereas sol–gel route with dip coating method was followed for titania coating. The adherence of the coating was evaluated by ASTM D3359 standard, and the composition of the duplex coatings was evaluated by X-ray photoelectron spectroscopy. The experimental parameters, namely, bath composition, temperature, immersion time and withdrawal speed of the specimens, were optimised to get homogeneous adherent coating. The localised corrosion resistance of ceria, titania and duplex coatings in sea water was studied by potentiodynamic anodic polarisation experiments. These coatings were characterised also by optical and scannning electron microscopes for analysing their pit morphologies. Duplex coated 304 SS exhibited superior corrosion resistance, and the probable reason for the improvement is discussed in detail in this investigation.

Enhancement of Corrosion Performance of Titanium by Micro-Nano Texturing

The present study reveals the influence of different anodizing electrolytes on the superhydrophobic surface modification of titanium and the resultant corrosion and biofouling resistance. Inspired ...

Studies to control biofilm formation by coupling ultrasonication of natural waters and anodization of titanium

The main objective of this study was to investigate the combined effect of ultrasonication of natural waters and anodization of titanium on microbial density and biofilm formation tendency on titanium surfaces. Application of 24 kHz, 400 W high power ultrasound through a 14 mm horn type SS (stainless steel) Sonicator with medium amplitude of 60% for 30 min brought about three order decrease in total bacterial density of laboratory tap water, cooling tower water and reservoir water and two order decrease in seawater. Studies on the effect of ultrasonication on dilute pure cultures of Gram-negative and Gram-positive bacteria showed five order and three order decrease for Pseudomonas sp. and Flavobacterium sp. respectively and two order and less than one order decrease for Bacillus sp. and Micrococcus sp. respectively. Ultrasonication increased lag phase and reduced logarithmic population increase and specific growth rate of Gram-negative bacteria whereas for Gram-positive bacteria specific growth rate increased. Studies on the biofilm formation tendency of these ultrasonicated mediums on titanium surface showed one order reduction under all conditions. Detailed biofilm imaging by advanced microscopic techniques like AFM, SEM and epifluorescence microscopy clearly visualized the lysed/damaged cells and membrane perforations due to ultrasonication. Combination of ultrasonication and anodization brought about maximum decrease in bacterial density and biofilm formation with greater than two order decrease in seawater, two order decrease in Bacillus sp. culture and more than four order decrease in Flavobacterium sp. culture establishing the synergistic effect of anodization and ultrasonication in this study.

Superhydrophobic coating on modified 9Cr – 1Mo ferritic steel using perfluoro octyl triethoxy silane

Lotus leaves are a typical example of superhydrophobic surface. Numerous studies have confirmed that surface morphology possessing micro- and nanoscale roughness along with a low surface energy material coating leads to apparent water contact angle (WCA) ⩾150°. In nuclear power plants, modified 9Cr–1Mo ferritic steel is the favoured steam generator tubing material. During transit, storage and installation, SHP surface on modified 9Cr–1Mo ferritic steel can impart good corrosion resistance to retain the integrity of the specimen during operation. In this study, SHP surface of modified 9Cr–1Mo ferritic steel with a WCA of 150±1° was successfully achieved by polishing, etching, perfluoro octyl triethoxy silane coating and baking. The WCA and contact angle hysteresis were measured. The surface morphology and the composition were characterised by atomic force microscopy and attenuated total reflection–infrared spectroscopy respectively. Superhydrophobicity and its related theories are also discussed in this paper.

2-Mercaptobenzothiazole-Loaded Hollow Mesoporous Silica-Based Hybrid Coatings for Corrosion Protection of Modified 9Cr-1Mo Ferritic Steel

The present work describes the development of an active corrosion protection system consisting of organic-inorganic hybrid sol-gel coating impregnated with inhibitor-loaded nanocontainers. Hollow m...

A silver nanoparticle loaded TiO2 nanoporous layer for visible light induced antimicrobial applications.

A nanoporous TiO2 layer was formed on commercially pure titanium by a simple anodization method in aqueous hydrofluoric acid (HF) medium. Silver nanoparticles (AgNP) were loaded into the nanoporous TiO2 layer by UV light irradiation. The morphology, chemical composition and photocatalytic activity of the modified titanium surfaces were characterized by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and UV-vis absorption spectroscopy techniques. The redox behavior of the AgNP loaded TiO2 layer was analyzed by cyclic voltammetry (CV) studies. The impedance behavior of the nanoporous TiO2 layer with and without AgNP was investigated by electrochemical impedance spectroscopy (EIS). The antibacterial effect of the AgNP loaded TiO2 layer was evaluated using Pseudomonas sp. and Bacillus sp. cultures. The efficacy of this modified layer to act as an antibacterial agent to minimize biofouling of titanium is demonstrated in this investigation.

Studies of detailed Biofilm characterization on fly ash concrete in comparison with normal and superplasticizer concrete in seawater environments

In cooling water systems, many concrete structures in the form of tanks, pillars and reservoirs that come in contact with aggressive seawater are being deteriorated by chemical and biological factors. The nuclear industry has decided to partially replace the Portland cement with appropriate pozzolans such as fly ash, which could densify the matrix and make the concrete impermeable. Three types of concrete mixes, viz., normal concrete (NC), concrete with fly ash and superplasticizer (FA) and concrete with only superplasticizer (SP) were fabricated for short- and long-term exposure studies and for screening out the better concrete in seawater environments. Biofilm characterization studies and microscopic studies showed excellent performance of FA concrete compared to the other two. Laboratory exposure studies in pure cultures of Thiobacillus thiooxidans and Fusarium oxysporum were demonstrated for the inhibition of microbial growth on fly ash. Epifluorescence and scanning electron microscopic studies supported the better performance of the FA specimen. Thus, the present study clearly showed that FA concrete is less prone to biofilm formation and biodeterioration.

Microbiologically Influenced Corrosion in UNS S31653: Detection and Analysis Using Electrochemical Noise Technique

Abstract Austenitic stainless steels are susceptible to microbiologically influenced corrosion (MIC), and biofilms of slime-forming bacteria can affect the integrity of the passive film of the stainless steel components. An attempt was made to detect and analyze the MIC on UNS S31653 using electrochemical noise (EN) technique. The progress of MIC was monitored in natural reservoir water, concentrated with biofilm-forming microbes along with 0.5 M sodium chloride (NaCl) and nutrients, as well as in a similar media minus microbes (made sterile by autoclaving) using two nominally identical UNS S31653 cylindrical specimens for about 3 weeks, where current and potential noise signals were collected at 1 Hz sampling frequency. Analysis of the shot-noise parameters like frequency of corrosion events, average charge in each event, true coefficient of variation, and noise resistance showed that initiation and propagation of MIC was marked by significant changes in these parameters. The presence of crevice corrosio...

Effect of biofouling on anodized and sol-gel treated titanium surfaces: a comparative study

Anodization and sol-gel treatments of titanium (Ti) were evaluated as biofilm control measures on surfaces exposed to seawater exposed to ultraviolet light. Anodized and sol-gel treated specimens were characterized using Raman spectroscopy to confirm the presence of TiO2. The single anatase phase was observed at the anodized surfaces whereas the anatase/rutile mixed phase was detected on the sol-gel coated surfaces. After exposure of the specimens to seawater, biofilms were characterized by total viable counts, and epifluorescence and Raman microscopy. These techniques confirmed the reduction in biofilm formation on both the anodized and sol-gel coated Ti specimens compared to the untreated specimens. Biofilm control by anodization was found to be more effective than by sol-gel treatment of the specimens. The higher particle size and the inhomogeneity at the sol-gel coated surfaces produced less effective biofilm control.